I. Technical Field
The present invention relates to a vibration power generator, a vibration power generating device, and a communication device having the vibration power generating device mounted thereon. In particular, the present invention relates to a static induction vibration power generator using an electret, a vibration power generating device, and a communication device having the vibration power generating device mounted thereon.
II. Description of the Related Art
A static induction vibration power generating device in which electric charges are provided to one electrode of a variable capacitance, and the electrode charges are induced to the opposed electrode by a static induction, a change in the induced electric charges is brought about by a change in capacitance, and the change in the electric charges is extracted as electrical energy, has been already proposed (refer to, for example, JP 2005-529574A (P. 10 to 11, FIG. 4) shown below).
FIG. 14 shows a static induction vibration power generator described in the aforementioned JP 2005-529574A (P. 10 to 11 FIG. 4). FIG. 14 is a schematic cross-sectional view of a vibration power generator 10 using an electret.
The vibration power generator 10 is composed of a first substrate 11 having a plurality of conductive surface regions 13 and a second substrate 16 having a plurality of electret material regions 15. The first substrate 11 and the second substrate 16 are disposed so as to have a predetermined clearance each other. The second substrate 16 including the electret material regions 15 is fixed. The first substrate 11 including the conductive surface regions 13 is coupled to a fixation structure 17 through springs 19. The springs 19 are connected to the both side surfaces of the first substrate 11, and also connected to the fixation structure 17. The first substrate 11 is capable of returning to its home position due to the springs 19, or the first substrate 11 makes a lateral motion (for example, an X-axial motion) to be capable of returning to the home position. This movement brings about increase and decrease of the overlapping area between the electret material regions 15 and the opposed conductive surface regions 13, which results in a change of electric charges in the conductive surface regions 13. A static induction vibration power generator performs electrical generation by extracting the change of electric charges as electrical energy.
However, in the static induction vibration power generator of FIG. 14, the first substrate is regulated so as not to vibrate in the directions other than the direction of the X-axis (the direction of an arrow 18 in the drawing). Therefore, this static induction vibration power generator 100 is incapable of extracting external vibrations in the directions other than the direction of the X-axis as electrical energy. In order to solve the problem, a static induction vibration power generator which is capable of utilizing external vibrations in many directions for electrical generation is proposed (refer to, for example, JP 2008-86190(P. 6 to 7, FIG. 6) shown below).
FIGS. 15(a) and (b) show a static induction vibration power generator described in the aforementioned JP 2008-86190(P. 6 to 7, FIG. 6). FIG. 15 are schematic cross-sectional views of a vibration power generator using an electret.
In a vibration power generator 20 shown in FIG. 15, an electret electrode 22C and a variable electrode 25C respectively include a plurality of electrode pads 22L and 25L which are arranged in a two-dimensional array. Therefore, it is relatively easy to equalize an amount of change in an overlapping area between the variable electrode 25C and the electret electrode 22C, which is brought about when the variable electrode 25C moves by a predetermined distance only in the direction of the X-axis (arrows 27a) to an amount of change in the overlapping area which is brought about when the variable electrode 25C moves by the predetermined distance only in the direction of the Y-axis (arrows 27b). Further, the vibration power generator shown in FIG. 15 has a structure in which it is possible to equalize the amounts of electricity generated when moving by a same distance in the direction of the X-axis and the direction of the Y-axis, to be capable of performing electrical generation responding to external vibrations not only in the direction of the X-axis, but also in the direction of the Y-axis.
The electret itself is already known. For example, an organic high molecular weight polymer (FEP (copolymer of tetrafluoroethylene and hexafluoroethylene)) is already known as a material for an electret. Further, a silicon dioxide film is known as an inorganic material, and further, a configuration in which a silicon dioxide film is covered with an insulating film to prevent electric charge leakage is proposed (refer to, for example, WO 2005/050680 (P. 2, FIG. 3) shown below).